Treatment of slag



Ju e 16, 1936. T. BARTHOLOMEW 2,044,199

TREATMENT OF SLAG Filed Sept. 9, 1932 5 Sheets-Sheet l (9) Vl/VVVVVVJ/ vvvvvvvvv 36 42 C v v vgvvvl N EV/AV/AM/A A A 1 June 16, 1936. T. BARTHOLOMEW 2,044,199

1 TREATMENT OF SLAG Filed Sept. 9, 1932 5 Sheets-Sheet 2 INVENTOR Z? @W Mm, v

Jun 16, 1936. r. BAR THOLOMEWV 2,044,199 7 TREATMENT OF SLAG I Filed Spt. 9, .1932 5.Sheets-Sheet4 Patented Jane 16, -l36 Uhlllhh stares PATENT @FFEQE 6 @llaims.

This invention relates generally to the treat,- ment of slag and the production therefrom of new and more desirable products. It relates more particularly to a process and apparatus for the a more efiicient disposition of molten blast furnace slag to produce marketable products of controllable high quality which have characteristics rendering them particularly suitable for construction purposes, and to the products.

to In the accompanying drawings, which illustrate preferred apparatus for carrying out the process,

Figure 1 is a schematic showing of the whole apparatus;

115; Figure 2 is a side elevation of a slag casting machine;

Figure 3 is a transverse section taken in a plane corresponding to the line III-HI of Fig ure 2;

an Figure 4 is an end elevation illustrating the drive for the casting machine;

Figures 5, 6 and 7 are, respectively, a plan view, a side elevation, and a section on the line VII-VII of Figure 6, of a lower mold;

25 Figure 8 is a plan view showing the arrangement of several lower molds;

Figures 9, 10 and 11 are, respectively, a plan view, a side elevation partially in cross-section, and a section on the line X[m of Figure 10,

30 of an upper mold;

Figure 12 is a perspective view of the piping for water cooling the molds, and

Figure 13 is a perspective view of a cast slag block made according to the invention.

35 Properly prepared iron blast furnace slag is nearly an ideal structural material. It is highly resistant to acids, alkalies, and weathering. It successfully withstands higher temperatures than do most natural rocks such as limestone,

dolomite, granite, quartz or gravel. Its crushing strength is extremely high, being of the order of 30,000 pounds per square inch While its true specific gravity is about 3.0, it normally contains an appreciable volume of more or less enclosed 45 pores which reduce its unit weight to well under that of competing materials.

Several 'millions of dollars are expended annually in the United States for disposal of the slag which necessarily is made in iron blast fur- 59 naces along with the iron. Although this slag is potentially valuable for construction purposes, only a comparatively small portion of its value is recovered by the sale or use of the relatively crude non-uniform and imperfectly adapted material 55 which is now produced.

( Dl. Edi-77.5)

When slags from modern iron blast furnaces are allowed to solidify, they normally undergo a certain amount of volume change. This is probably caused by the separation of part of the dissolved gases during solidification. This volume change ordinarily results in marked deformation of one of the surfaces of a cast slag product and not infrequently in the complete rupture of such a surface and the spewing out of molten slag from the interior. This difficulty has prevented the commercial preparation of such slags by casting, but is overcome in my process.

I have discovered how to economically treat molten slag to obtain a product of greater uniformity and. higher quality than could be obl5 tained by methods known heretofore. Not only can I produce material which is substantially uniform as to pore content, apparent specific gravity, unit weight and strength, but I can produce it in uniform or graded sizes without crushing go or screening and in exactly those shapes which are best suited for the particular purpose for which it is to be used. Furthermore, I can, within limits, controllably vary. the pore content, unit weight and strength to still further adapt the product to special uses.

In my process, I prefer to charge the molten slag into strongly cooling metal molds which contact with all surfaces of the molten slag body and quickly solidify crusts on all surfaces of the .30 casting so that no one crust is substantially weaker than at least one other crust. Thereafter, with minimum loss of heat, I quickly discharge the casting from the mold, after which I can handle the still largely molten material as discrete solid bodies which may be annealed and cooled for use. Y

I have discovered that I can avoid the rupture or spewing out of molten slag and can prevent extreme deformation of a surface of the cast ar- 40 ticle by distributing any unavoidable deformation over a plurality of the surfaces of the article. This can be done by casting the slag in such shape and in such manner that after removal of the casting from the mold and during solidification of its interior, no one crust is substantially more deformable than at least one other crust.

This result is accomplished preferably by casting the slag into an article having its principal surfaces substantially alike in size and shape, each surface being formed by contact for equal time with a mold surface of equal heat capacity, conductivity and cooling power. However, I do not confine myself to shapes with like surfaces, nor to the equal cooling of the surfaces, nor to equal contact times between slag and mold surfaces, nor to individual mold surfaces having like cooling characteristics. Any or all of these factors may be varied so long as a plurality of surfaces of the freshly cast article are deformable without rupture and no one surface is substantially weaker than at least one other surface at the time the internal pressure is relieved.

Swelling, which .is the most common form of deformation, cannot take place until the article leaves the mold. Thereafter, rupture during cooling is prevented and distributed deformation is facilitated by having the crusts as thin and as readily deformable as possible and yet retain the interior fluid slag during the solidification thereof. This condition is best obtained by using cold molds which are prevented from overheating while in contact with the slag. I, therefore, pre-v fer to use metal molds and prevent their overheating during their short contact with the slag by providing ample thickness of metal in the molds to absorb the heat or by water cooling the molds, or preferably by both of these means.

The use of these cold molds is highly advantageous for several other reasons. By extracting heat very rapidly from the slag surfaces, these molds set up a high temperature gradient in the surfaces of the slag and although they extract heat at a high rate, they actually extract the minimum quantity of heat necessary to produce the desired crust. By extracting a smaller quantity of heat than would any other type of mold, they permit the cast slag body to retain the maximum quantity of heat and, therefore, to automatically reheat its own crusts sufiiciently to permit deformation without rupture and to thoroughly anneal them without the addition of more heat. Furthermore, the use of the highly cooled molds which extract heat very rapidly, but in smaller quantities than would be required with other molds, permits extremely rapid discharge from the molds and thereby speeds up the whole operation, reducing the size and cost of equipment, the working space needed, and simplifying the whole operation. Instead of requiring a dwell of several minutes in the mold, as was required in the now obsolete pan casting process, or several hours or even days as contemplated in some other processes, I am able to discharge'most of my products from the mold after a dwell 'of only to 30 seconds.

The time that the slag remains in my mold depends upon the size of articles which are being cast. The slag is maintained in the molds only long enough to develop surface crusts which will permit handling, which surface crusts inevitably grow thicker and stronger during handling. The dwell in the molds should not be unduly extended as it is desirable to retain in the articles sufficient heat so that after discharge from the molds and delivery to an annealing chamber where the temperature gradient in the surfaces is eliminated, the average temperature of the article will still be safely above its annealing point in order that the crusts will be deformable without rupture, and maximum toughness may be developed. Since the annealing point of blast furnace slag is about 900 0., it is preferred to govern the time that the slag is in the mold so that there will be a solidified crust sufliciently strong to contain the fluid interior of the articleduring handling, and yet extract only such an amount of heat from the casting that its average temperature will still be above its annealing point of about 900 C. For -.or 2'' cubes, I have found that 5 to 15 secends is a suflicient time to maintain the slag in the molds. For larger castings, the dwell will be longer, and for smaller castings, it will be shorter. In casting larger pieces especially from very hot slag, it is possible to retain so much heat 5 in the product passing to the annealing chamber that the average temperature may become too high and the articles stick together. I avoid this difficulty by supplying additional cooling if necessary to the slag articles as they are conveyed from the molds to the annealing chamber. After discharging the castings from the molds, I may deliver small articles directly to a stock pile if highest quality is not required, but for most purposes I prefer to anneal and slowly cool the product as by passing it into an annealing chamber such as a silo in which the bodies may contact with each other, the surface crusts be reheated at least to the annealing point of the material and any internal stresses be relieved by viscous flow. Thereafter, the product can readily be cooled to a safe shipping temperature by passing air through the material preferably in a direction counter to the movement of the slag articles. The necessary time for this annealing and cooling depends largely upon the size and shape of the'pieces and upon the quantity of air used for cooling. With material of 1" 'to 2" size, first-class results can be obtained in about 1 to 5 hours.

The product made by the above described process is not weak and friable as is granulated slag.

It differs from pan slag in that it contains no brittle, glassy, or granular material, but is uniformly devitrified and tough. It difiers from ordinary air cooled slag in uniformity, in quality, and in shape. Instead of being irregularly purous, each piece is of practicaly the same specific gravity and in general is heavier, denser, and stronger than is ordinary air cooled slag made from the same flush or cast.

However, I can vary and control this density within limits. By using dry molds and avoiding unnecessary agitation or contact of water with the molten slag, I obtain a very dense product. By agitating the slag before charging into the molds or by casting in wet molds, I can obtain a very marked decrease in apparent specific gravity. By foaming the molten slag as disclosed in Sem Patent No. 1,471,421, granted October 23, 1923, or in my Patent No. 1,901,891, granted March 21, 1933, the porosity can be considerably increased so that it is possible to produce my product not only in the sizes and shapes desired,

but also in the weight and strength desired. When fractured surfaces are essential, my product can be made large, and crushed. If, as is usually the case, fractured surfaces are not essential nor even desirable, I cast the slag to both 00 size and shape desired and avoid any necessity for crushing and screening.

Referring more particularly to the accompanying drawings, and for the present especially to Figure 1, which illustrates in a diagrammatic manner the whole apparatus, the slag which is to be treated is tapped from a blast furnace 2 into a ladle 3 and is poured from the ladle on a chute 4 which feeds it to a slag casting machine indicated generally by the reference numeral 5. The slag casting machine comprises a series of lower molds 6 and a series of upper molds I, each mounted on an endless conveyor, the upper and lower molds cooperating with each other so as to contact with all surfaces of the slag which is introduced into the molding machine. The lower molds form the bottoms and sides of each article and the top molds form the top surfaces of the articles, the arrangement being such that thin crusts are formed on all surfaces of the slag body, which crusts enable handling of the blocks even though their interiors are still molten. The blocks are discharged from the casting machine and slide down a chute 8 into the buckets of a bucket conveyor 9 which elevates them and then discharges them through a chute i into an annealing chamber I l formed in the shape of a silo. The separate or discrete cast slag bodies i2 are illustrated as they slide down the chute it into the annealing chamber.

The blocks, although having solid crusts on each of their surfaces, are still fluid in their interiors, the heat of the molten interiors acting to reduce the temperature gradient in the surfaces of the blocks as they pass through the annealing chamber, the thickness of the crusts formed on the blocks being controlled so that the average heat in the blocks is suflicient to anneal them. The blocks pass downwardly through the annealing chamber and are discharged from the bottom thereof into a car i3, the chamber being provided with a discharge gate, not shown. The bottom of the annealing chamber may be provided with windows it so that air may be drawn upwardly through the pile of blocks in the annealing chamber by a suction fan i5 arranged in the stack 16.

As shown more particularly in the other figures, the casting machine comprises a series of lower molds 6 mounted on an endless chain it which passes around sprockets i5 secured at each end of the machine to shafts mounted in bearings supported by a framework 2|. One of the shafts Ed has a gear 22 secured thereto which is driven by a motor 23 through a worm 26, thereby moving the lower molds B in the direction indicated by the arrow.

A series of upper molds i is connected to an endless chain 28 which passes around sprockets 29 mounted at each end of the machine on shafts 30. The left-hand sprocket 29, as viewed in Figure 2, is driven through a chain 38 which passes around a sprocket 32 secured to the shaft 30, the other end ofthe chain 39 passing around a sprocket 33 secured to ashaft 3%. Also secured to the shaft 35 is a gear 35 which meshes with a gear 35 whichis secured to the shaft'Zil. By this arrangement, when the motor 23 is in operation, the upper and lower gmolds l and 6 are brought into cooperative relationship with each other, so that the bottom moldsform the bottom and sides of the slag block and the upper molds form the top of the block. Molten slag is introduced into the bottom molds by the chute i, and after having been acted upon by the upper and lower molds which form crusts on all of the surfaces of the block-the block is discharged from the right-' hand end of the machine by the spreading apart of the lower molds as they pass around the righthand sprocket it.

The construction of the lower molds is illustrated in detail in Figures 5 through 8. Referring to these figures, the molds extend transversely of the direction of travel and are provided on each side with molding cavities 38, the cavity for forming an entire article being partially in each of two adjacent molds. By the use of split molds, when the molds pass around the right-hand sprocket E9," the molds are spread one of the upper molds fits directly on top of the cavities in the lower molds so that an upper and two lower molds taken together completely enclose and form solid crusts on all of the surfaces of the slag block.

In order to insure that the upper and lower molds will cooperate accurately, each ofthe upper molds l is provided at each end with a tooth M which fits between pins :32 secured to the ends of each of the lower molds 6. Although the main drive of the upper molds is through the chain 3!, the use of the teeth 6! and the pins 62 on the upper and lower molds, respectively, insures that in operation the upper and lower molds will fit accurately together.

As shown in Figure 10, the upper side of each upper mold I is provided with a channel or recess 33 into which water may be sprayed in order to cool the mold. Water is preferably used to cool both the upper and lower molds, one arrangement of piping which may be used being shown in Figures 2, 3 and 12. Water is supplied through a header t5 and crosspipes 66 to pipes ill, 68 and as which extend longitudinally of the direction of movement of the molds. water into the channels 43 formed in the rear surfaces of the upper molds, whereas the pipes W and ie are used to cool the surfaces of the lower molds. The spray discharging onto the upper molds is of larger capacity to insure that the upper crust of the article will be at least as strong as the crusts formed in the lower molds.

The lower molds 6 are supported in their upper run on inverted T-irons so as to maintain them accurately in a horizontal plane. Sometimes solid material such as solidified slag may be delivered over the chute d to the molds. In order to prevent such solid material from breaking the casting machine, the upper molds l are arranged so that they may ride over the solid matter. This is accomplished in the present embodiment by providing the angles which support the upper molds with pins 56 which fit into slots 5i formed in the upper ends of vertical supports 59. This arrangement enables the left-hand end of the series of upper molds to rise and allow any solid material to pass under that end of the series of upper molds, the angles 55 pivoting at this time on the right-hand pins 56, and thereafter as the solid material passes along the casting machine, the right-handend of the frame formed by the angles 55 rises by pivoting on the left-hand pins 56. In this manner, breakage .of the machine is prevented, even though solid material is delivered with the slag to the molds.

The slag blocks having solidified crusts on all of their surfaces due to contact therewith of the upper and lower molds, are delivered from the casting machine when the lower molds pass around the right-hand sprocket it which spreads the molds apart. At this point in the process, the surfaces of the blocks are solid, but the interiors are fluid. They are then transported by the bucket elevator, as shown in Figure 1, or by some The pipes 61 spray 3 other suitable means to the annealing chamber M W wherein the temperature gradient in the surfaces of the blocks is gradually reduced and the interiors allowed to solidify. If desired, air is blown through the stack of blocks in the annealing chamber, and after the blocks have cooled to more nearly atmospheric temperature, they are delivered from the bottom of the annealing chamber into cars l3 and are ready for use.

I'have illustrated and described the present preferred embodiment and manner of practicing my invention. It is to be understood, however,

that the invention may be otherwise embodied or practiced within the scope of the following claims.

I claim:

1. The process of treating slag which tends to expel gases and develop internal pressure during solidification, which comprises surrounding a body of highly fluid molten slag with contacting cooling mold surfaces which form crusts on all surfaces of the slag body so that the body may be handled while the interior thereof is still fluid.

2. The process of treating slag which tends to expel gases and develop internal pressure during solidification, which comprises pouring highly fluid molten slag into a mold which contacts all surfaces of the slag body to form surface crusts which enclose the fluid interior of the slag body, removing the slag body from the mold while the interior of the body is fluid, and solidifying the interior of the body while no one surface crust is substantially weaker than at least one other surface crust.

interior has solidified, bringing a plurality of the 10 external surfaces of the article to a deformable condition during solidification of the interior of the article, and cooling the article.

5. In the method of preventing rupture of an article cast from slag which tends to expel gases l5 and develop internal pressure during solidification, the step which comprises bringing a plural- I ity of its external surface crusts to a deformable condition during solidification of its interior, whereby the change in volume of the article during solidification of its interior may be distributed over a plurality of said surfaces without rupture. 6. The process of treating slag which tends to expel gases and develop internal pressure during solidification, which comprises surrounding a 25 small body of highly fluid molten slag with contacting cooling mold surfaces which form crusts of substantially equal areas on all surfaces of the slag body so that the body may be handled while the interior thereof is still fluid. 30

TRACY BARTHOLOMEW. 

